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Work/Energy problem at an angle

  1. Feb 7, 2012 #1
    1. The problem statement, all variables and given/known data

    In the figure below, a block of ice slides down a frictionless ramp at angle θ = 50°, while an ice worker pulls up the ramp (via a rope) with a force of magnitude Fr = 60 N. As the block slides through distance d = 0.65 m along the ramp, its kinetic energy increases by 85 J. How much greater would its kinetic energy have been if the rope had not been attached to the block?

    2. Relevant equations
    W=ΔEk
    W=F*d*cosθ

    3. The attempt at a solution

    First, I solved for the gravitational force in the X direction: (Fgx-60N)*.65m*cos50=85J
    Fgx = 263.44 N
    Then, I plugged it back into the work equation to see how much work would be done then: 263.44N*.65m*cos50=W
    W=110.06J=ΔEk
    110.6J-85J=25.6J
    Yet, this is not the right answer. What am I doing wrong?
     
  2. jcsd
  3. Feb 7, 2012 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The x-component of gravity and the 60 N force are already parallel to the ramp, so no need for the cos50 factor.
     
  4. Feb 7, 2012 #3
    Wow. That was a silly mistake. Thank you! :)
     
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